ANODIC  POTENTIALS 

A STUDY  OF  THE  ANODIC  BEHAVIOR  OF 
COPPER  AND  MERCURY 

BY 

HAYES  TRYFORD  DARBY 
B.  S.  Ohio  State  University 
1912 

THESIS 

Submitted  in  Partial  Fulfillment  of  the  Requirements  for  the 

Degree  of 

MASTER  OF  SCIENCE 
IN  CHEMISTRY 

IN 

THE  GRADUATE  SCHOOL 

OF  THE 

UNIVERSITY  OF  ILLINOIS 
1921 


« 


V 


UNIVERSITY  OF  ILLINOIS 


THE  GRADUATE  SCHOOL 

jJ une  4 . 1 92 L_ 

I HEREBY  RECOMMEND  THAT  THE  THESIS  PREPARED  UNDER  MY 

SUPERVISION  BY HM.e-.s . J ■ rV f-9g jLJtejjgZ 

Anodic  Potentials*  A Study  of  the  Anodic 

Behavior  cf  Copper  and  Mercury 

BE  ACCEPTED  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR 
THE  DEGRFE  OF  Master  of  Scj enc e In  Chemistry, 

In  Charge  of  Thesis 

mC  J.  

Head  of  Department 


Recommendation  concurred  in* 


Committee 

on 

Final  Examination* 


*Required  for  doctor’s  degree  but  not  for  master’s 


Digitized  by  the  Internet  Archive 

in  2015 


https://archive.org/details/anodicpotentialsOOdarb 


TABLE  OF  CONTENTS 


: age . 

I .  Introduction  2 . 

II.  Experimental 

1. The  Determination  of  Reaction  Potentials  4. 

2.  Aparatus  4. 

3.  Experimental  Procedure  5. 

4 . Potentials of  Copper  with  (a)  II2PO4  in  H20,(h)  KEr 

in  II2O,  (c)  KCl  in  N/l  NH4NO3,  (d)  Kl  in  »/l  NH4N0r,  7. 

5.  Potentials  of  Hercury  with  (a)  KCl,(t$  KBr,(c)  KI 


all  in  N/l  NH4NO3. (d)  H2S04  ia  H20.  14. 

5. Reaction  Potentials  and  Dilution.  18. 

III . DISCUSSION. 

1.  Reaction  Potentials  for  Zero  Current.  19. 

2.  Products  of  the  Anode  Reaction.  20. 

".Form  of  the  Currents Potential  Curves.  20. 

4.  The  Relation  he tween  Reaction  Potential  and  Concen- 
tration. 21. 

5.  The  Existance  of  Definite  Ionization  Potentials.  21. 

IV.  SUMMARY  23. 


1 


ACKNOWLEDGMENT. 


I wish  to  thank  Doctor  J.K. Reedy  for  his  assistance  in  the  sug- 


gestion and  direction  of  the  work  outlined  in  the  following  pages. 


Hayes  Tryford  Darby. 


2 


INTRODUCTION. 

The  object  of  this  work  was  to  determine  something  of  the  anod- 
ic behavior  of  the  two  metals , copper  and  mercury.  This  has  been  done 
by  determining  the  electrode  potentials  of  these  two  metals  in  sever- 
al electrolytes  and  at  various  dilutions. 

The  mechanism  of  an  anode  reaction  may  be  hypothetically,  as- 
sumed to  be  of  two  general  types, viz.  (1$  discharge  of  anions,  (2) 
the  formation  of  cations.  Thermodynamic  considerations  throw  no  light 
on  this  problem  , since  the  results  depend  wholly  on  the  initial  and 
final  states  and  ure  "independent  of  the  path". 

If  a metal  is  made  the  anode  in  an  electrolytic  cell  and  a 
progressively  increasing  potential  applied, flexures  may  appear  in  the 
current  potential  curve,  (See  B and  C in  Figure  !•)* 


These  flexures  are  best  explained  as  follows:  The  curve  AB  rep- 
resents the  relation  that  exists  between  current  and  potential  for 
low  values  of  the  latter.  However  as  the  potential  is  increased  a 
sort  of  limiting  value  for  the  current  is  reached, Be . This  is  due  to 
fact  that  the  process  consists  in  the  discharge  of  anions  and  the 
speed  of  the  reaction  is  limited  by  the  speed  with  which  these  anions 
are  brought  up  to  the  anode  by  diffusion  and  stirring.  As  the  potent- 
ial is  pressed  still  higher  there  is  a flattening  of  the  curve  and 


_ 


3 


later  another  flecture  is  found  at  C.  Here  another  reaction  is  super- 
imposed upon  the  first  one  either  due  to  the  fact  of  the  direct  ion- 
ization of  the  anode  or  to  some  new  anion  (say  the  Oil  of  the  water]' 
is  now  being  discharged.  Le  Blanc  reports  in  "Elec trochemis try" 

(1910)  page  307, that  he  has  detected  four  flexures, and  he  has  at- 
tributed them  to  the  begining  of  a new  and  definite  electrode  react- 
ion. It  is  to  be  frankly  conceded  that  a curve  with  a double  flexure 
may  be  explained  without  invoking  the  hypothesis  of  primary  ioniza- 
tion of  the  metal.  The  first  curve  may  be  due,  we  wrill  say,  to  the 
discharge  of  the  anion  of  the  electrolyte  and  the  second  to  the  dis- 
charge of  the  OH  of  the  water. 

In  cases  where  the  anode  reaction  results  in  the  formation  of  an 
insoluble  subs tance, the  result  is  much  more  conclusive.  For  example, 
the  electrolysis  of  halide  solutions  on  silver  anodes, com pact, adher- 
ent deposits  of  silver  halide  form  upon  the  anode.  If , however, the 
halide-ion  concentration  is  low  so  that  the  anode  potential  may  be 
given  a high  value, the  silver  halide  forms  as  a precipitate  within 
the  solution  and  not  on  the  anode.  The  must  direct  explanation  of 
this  behavior  i.s,that,at  high  potentials  silver  is  capable  of  direct| 
ionization. (See  Amer . Jour .Sci*  vol.  40  (1915)  page  281.). 

A more  or  less  presumptive  evidence  of  the  direct  ionization  of 
metals  is  found  in  their  cathode  behavior.  It  is  hard  to  postulate 
any  explanation  of  the  plating  out  of  a metal  on  the  cathode  that 
does  not  involve  direct  ionization.  Since  such  reactions  are  revers- 
ible, and  since  no  other  cation  than  the  II  ion  from  the  solvent 
wat 

water  may  be  available, it  seems  highly  probable  that  such  direct 
ionization  may  be  a normal  behavior. 


• . 

. 


■ 


- 


- 


t 


. 


' 


1 


, 


' 


Thus,  in  order  to  throw  possibly  some  light  on  this  problem  of 
direct  ionization  the  following  work,  involving  the  behavior  of  anod- 
es of  coxiper  and  mercury,  has  been  carried  out. 

THE  DETERMINATION  OF  THE  REACTION  POTENTIALS. 

Hy  definition  the  reaction  potential  of  a substance  is  the  pot- 
ential difference  that  must  exist  between  that  substance  and  a solu- 
tion in  order  that  a reaction  may  begin.  This  potential  difference 
can  be  best  determined  by  making  the  substance  one  of  the  electrodes 
of  an  electrolytic  cell  and .measuring  the  potential  at  which  a cur- 
rent just  begins  to  flow.  The  third  electrode  method  was  used  through- 
out this  work. 

APPARATUS . 


5. 


Figure  2.  is  a diagram  of  the  apparatus  used.  The  electrolytic 
cell  ® was  a glass  clylinder  about  four  and  one  half  inches  high  and 
two  and  one  hallt  inches  in  diameter.  It  was  closed  by  a rubber  stop- 
per through  which  passed  the  stem  of  the  mechanical  stirrer  and  con- 
nections for  the  electrodes.  The  cathode  P was  a piece  of  bright  plat- 
inium  29  x 30  mm.  The  anode  C was  of  sheet  copper  20  £ 30  mm.  and 
was  freshly  copper  plated  from  a solution  of  copper  sulphate  acidifi- 
ed with  a little  nitric  acid.  In  the  experiments  with  mercury  a simu- 
lar  cell  was  used,  the  mercury  forming  a layer  in  the  bottom  of  the 
cell  suitably  connected  by  means  of  glass  tubes  and  sealed  in  xvires. 

The  main  circuit  was  operated  by  a storage  cell  B as  indicated 
in  the  diagram.  A sensitive  galvanometer  G in  the  main  circuit  serv- 
ed as  a current  indicator.  With  currents  to  large  for  the  galvanomet© 
er  a Weston  milliammeter  N could  be  substituted  by  means  of  the 
switch  SI.  R is  a variable  resistance  by  means  of  which  the  electro- 
lytic current  could  be  varied.  D was  a third  electrode  (a  calomel  el- 

• . of 

ectrode)  and  E an  intermediate  vessal^some  electrolyte  to  eliminate 
diffusion  potentials.  For  this  purpose  N/l  iiCI  solution  was  used  in 
all  cases. 

In  the  subsidiary  circuit  B’  is  a lead  storage  cell  connected  as 
indicated  to  a potentiometer  Y.  M is  a standard  cadmium  cell  and  was 
used  through  out  as  a reference  cell.  T is  a taping  key  used  in  con- 
nection with  a D’Arsonval  galvanometer  0 in  establishing  a balance 

aTui 

on  the  potentiometer  S2,S3,S4,S5  are  switches  used  to  make  the  appat 
convenient . 

EXPERIMENTAL  PROCEDURE . 

Establish  balance  between  the  standard  cell  M and  the  battery  B’ 
by  throwing  switches  S3  and  S5.  Rote  this  reading  ofl  the  potentiomet- 


6 


er  as  the  reading  with  the  standard  cell.  Close  the  main  circuit  by 
means  of  switch  84  in  such  a mannor  that  current  will  pass  through 
the  electrolytic  cell  in  the  direction  opposite  to  that  desired  when 
taking  reeding.  Adjust  the  variable  resistance  until  a point  is 
reached  where  no  current  passes  through  the  cell  and  the  direction  of 
which  will  be  reversed  when  further  resistance  is  added  or  removed  as 
the  case  may  be.  Switches  S2  and  S3  and  SI  are  so  closed  that  the  cip 
cuit  is  complete  and  the  amount  of  current  can  be  read.  Ey  means  of 
the  potentiometer  establish  apoint  of  balance  by  bringing  the  galvan- 
ometer 0 to  the  zero  deflection  as  before.  Note  the  reading  on  the 
potentiometer  as  "reading  of  x-cell.  Increase  the  current  by  suitable 
steps  and  secure  readings  o£  the  balance  points  on  the  potentiometer. 
Record  current  and  voltage  thus  obtained. 

CALCULATIONS . 


Readings  obtained. 

Against  standard  ceJ)l,for  example  equals  0.S035  volts. 

Against  X-cell  for  example  equals  0.0688  volts. 

Known  voltage  of  standard  cell  equals  1.0184  volts. 

Known  voltage  of  third  electrode , equals  0.2872  volts 

Then  1.0184  : 0.6035  ::  X : 0.0688,  X - 0.0688 

0.6035 


X equals  voltage  of  X-cell. 

Voltage  of  Anode  equals  0.2872  - X equals  ¥ 


7. 

TABLE  1 

. Copper  Anode  and  Sulphuric  Acid  as  Electrolyte. 

This  table  gives  results  obtained 

using 

copper  as  the  anode  and 

sulphuric  acid  in 

water 

solution  as  the  electrolyte 

• c equals  cur- 

rent  in  divisions 

on  the 

galvanometer 

. v equals  potential  of  Anode 

in  volts. 

N/2  H2SO4 

/*V  ^ c -/  ry 

N/2 

H2S04 

N/4  H2S04 

c 

* V 

c 

V 

c 

V 

0 

0.217 

0 

0.223 

0 

0218 

1 

0.21S 

1 

0.223 

1" 

0.219 

2 

0.219 

2 

0.223 

2 

0.220 

3 

0.219 

3 

0.224 

3 

0.221 

4 

0.220 

4 

0.225 

4 

0.221 

5 

0.220 

5 

0.225 

5 

0.222 

6 

0.221 

6 

0.225 

6 

0.222 

7 

0.222 

3 

0.227 

7 

0.223 

8 

0.222 

10 

0.227 

9 

0.224 

11 

0.223 

12 

0.228 

10 

0.225 

15 

0.225 

14 

0.228 

12 

0.226 

20 

0.226 

16 

0.229 

15 

0.228 

24 

0.227 

13 

0.23  0 

19 

0.230 

29 

0.228 

25 

0.231 

23 

0.231 

50 

0.232 

29 

0.231 

27 

0.233 

100 

0.247 

50 

0.239 

50 

0.249 

100 

0.245 

100 

0.261 

The  results  contained 

in 

this  table  are 

shown  graphically  in 

Plate  4.  Current 

in  galv 

anometer  divisions 

plotted 

as  ordinates  and 

the  corresponding 

electrode 

potentials  as 

abscisae . 

Table  2. 

Copper  Anode 

and 

KBr  diss 

.olved 

in  Water 

as  Electrolyte. 

c 

6 current  in 

divisions  on 

the  g 

alvanometer . 

v= 

anode 

potentials 

in  volts 

• 

N/l  KBr. 

n/i 

EBr 

N/2  KBr 

N/&  KBr 

N/4  KBr 

c V 

c 

V 

c 

V 

c 

c V 

0 -0,070 

0 

-0. 075 

0 

wO.  048 

0 

-0.  052 

0 -0.019 

1 -0.067 

1 

-00071 

1 

-0.044 

2 

-0.  046 

3 0.010 

4 -0.064 

2 

-0.068 

4 

-0.1137 

3 

-0.041 

4 0.014 

5 -0.063 

4 

_0.  036 

9 

-0.029 

5 

-0.038 

9 0.023 

3 -0.031 

6 

-0.0S3 

14 

-0.023 

10 

-0.031 

14  0.032 

9 -0.058 

10 

-0.060 

18 

-0.  017 

15 

-0.025 

19  0.039 

12  -0.056 

15 

-0.056 

23 

-0.  012 

20 

-0. 019 

24  0.041 

14  -0,054 

20 

-0.053 

25 

-0.  009 

27 

-0.  013 

28  0.046 

22  -0.049 

24 

-0.051 

50 

0.012 

50 

0.  008 

50  0.066 

30  -0.045 

27 

-0.048 

100 

0.027 

100 

0.025 

100  0.088 

50  -0.029 

50 

-0.031 

100  -0.018 

100 

-0.020 

too. 


t 

vjj 

5: 

I 

N, 

Q 


A/ 

m 


//&  SOy 


50 


US 


<0 

£ 

* 

* 

CD 

\ 

S 

o 

t 


a.o 


jS 


/o 


o 


C) 


0 


<b 

o joo  i ,2.00  5 o 
po/evt/aJs  —+ 


Plate  No  l 

Copper  Anode 

da  SOy  in  Water 


7/00  9 Stop 

Parent/ a is  — > 


8 


Table  2 (continued). 

8/4  KBr.  N/S  KBr . N/S  KBr . N/l6  KBtt.  N/l6  KBr. 


c 

V 

c 

V 

c 

V 

c 

V 

c 

0 - 

■0. 016 

0 

0.010 

0 

0.024 

0 

0.062 

0 

0.  056 

1 - 

■ 0.015 

2 

0.019 

2 

0.040 

1 

0.  071 

1 

0.  037 

4 - 

0.014 

5 

0.027 

4 

0.  048 

5 

0.  099 

4 

0.  084 

8 - 

0.007 

10 

0.  037 

8 

0.  062 

10 

0.106 

10 

0.106 

12 

0.  002 

16 

0.  052 

13 

0.073 

15 

0.116 

15 

0.115 

17 

0.007 

22 

0.  079 

IS 

0.082 

21 

0.126 

21 

0.124 

20 

0.013 

28 

0.089 

25 

0.093 

25 

0.133 

27 

0.133 

25 

0.02  0 

50 

0.109 

50 

0.124 

50 

0.171 

50 

0.159 

50 

0.038 

100 

0.129 

100 

0.168 

100 

0.193 

100 

0.18S 

100 

0.  0G2 

w / oo 

I*/  t 

KBr 

N/  32 

KBr 

N / 34 

KBr 

N/64 

KBS 

N/l28KBr • 

C 

V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

0.090 

0. 

0.086 

0 

0.109 

0 

0.105 

0 

0.12  0 

2 

0.114 

1 

0.097 

1 

0.123 

1 

0.119 

1 

0.151 

4 

C$127 

4 

0.114 

4 

0.144 

5 

0.153 

4 

0.183 

10 

0.146 

9 

0.131 

9 

0.170 

11 

0.176 

10 

0.214 

15 

0.159 

15 

0.148 

13 

0. 188 

15 

0.195 

16 

0.246 

20 

0.166 

20 

0.153 

20 

0.200 

21 

0.2  09 

20 

0.258 

24 

0.175 

50 

0.196 

26 

0.211 

25 

0.216 

30 

0.270 

50 

0.215 

100 

0.237 

50 

0.250 

50 

0.277 

100 

0.260 

N /l28 

KBr 

N/256 

KBr 

N/256 

i KBr 

Vii2 

: KBr 

n/qc 

024-Br 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

9 

0.122 

0 

0.341 

0 

0.141 

0 

0.150 

0 

0.194 

1 

0.149 

1 

0.175 

1 

0.172 

1 

0.169 

1 

0.220 

5 

0.182 

5 

0.22S 

5 

0.223 

5 

0.199 

3 

0.242 

11 

0.214 

13 

0.261 

11 

0.200 

10 

0.216 

9 

0.266 

15 

0.235 

15 

0.230 

15 

0.282 

25 

0.269 

26 

0.247 

28 

0.315 

30 

0.277 

50 

0.252 

50 

0.376 

N/2048 

,:Br 

N/409 

5 KBr. 

c 

V 

c 

V 

0 

0.218 

0 

0.243 

3 

0.224 

1 

0.247 

6 

0.229 

3 

0.253 

10 

0.241 

9 

0.268 

14 

0.247 

17 

0.282 

20 

0.257 

22 

0.290 

26 

0.237 

28 

0.301 

50 

0.291 

50 

0.361 

100 

0.359 

100 

0.487 

Plate  Nf>  2 shows  typical  curves  from  the  above  data. 


: 


PJ<Lte  No  Z 

Copper  Anode- 

HBr  Tv  Waffa 


— ./O  0 


fJOo 


.3.0  o 


pQf&fftici/s  ?* 

3 00  MOO  ,560 


9 


Table  3.  Copper  Anode  In  an  Electrolyte  of  Potassium  Chloride 
Dissolved  either  in  Water  or  in  N/l  NH4NO3  Solution 


C = current  m galvanometer  scale  divisions. 
V = Electrode  potentials  in  volts. 


w denotes  that  water  alone  was 


N/l  KC 1'“* 

N/l  KC1* 

N/2  KCl* 

c 

c 

V 

e 

vv 

0 

-0.016 

0 

-0.010 

0 

0.028 

1 

-0.013 

5 

-0. 003 

1 

0.029 

8 

-0.007 

10 

0.  002 

3 

0.031 

14 

0.008 

14 

0.  009 

5 

0.034 

23 

0.010 

13 

0.  019 

10 

0.040 

50 

0.023 

23 

0.023 

13 

0.  045 

100 

0.041 

50 

100 

0.029 

0.046 

21 

26 

50 

0.053 
0.  058 
0^072 

N/8  KC1 

n/s 

KCl*b 

»/l6 

- KC1 

e 

e 

V 

c 

V 

0 

0. 067 

0 

0.062 

0 

0.117 

2 

0.071 

1 

0.070 

2 

0.120 

5 

0.  079 

4 

0.  077 

5 

0.124 

10 

0.090 

9 

0.  089 

9 

0.128 

14 

0.  099 

14 

0.100 

13 

0.132 

19 

0.106 

19 

0.107 

18 

0.136 

24 

0.113 

25 

0.115 

24 

0.138 

50 

0.140 

50 

0.143 

50 

0.162 

100 

0.160 

100 

0.161 

100 

0.174 

N/ 64 

: KC1 

N/ 64 

KC1 

N/ 12 

:8  KC1 

c 

V 

c 

V 

c 

V 

0 

0.133 

0 

0.166 

0 

0. 166 

2 

0.167 

1 

0.168 

1 

0. 168 

5 

0.171 

3 

0.169 

3 

0.158 

9 

0.174 

8 

0.174 

5 

0.174 

14 

0.180 

12 

0.177 

9 

0.182 

19 

0.186 

19 

0.183 

15 

0.188 

25 

0.192 

22 

0.186 

19 

0.195 

50 

0.203 

50 

0 2 09 

25 

0.2  01 

100 

0.227 

100 

0.225 

5:0 

100 

0.220 

0.233 

N/512  ACL 

N/512  KC1 

Isf/ 1 G24-KC1 

c 

V 

c 

V 

c 

V 

0 

0.196 

n 

U 

0.173 

0 

0.251 

1 

0. 198 

2 

0.181 

1 

0.253 

4' 

0.201 

5 

0.186 

5 

0.256 

11 

0.210 

9 

0.193 

10 

0.258 

14 

0.214 

11 

0.201 

15 

0.232 

20 

0.219 

14 

0.2  09 

19 

0.264 

25 

0.223 

20 

0.213 

50 

0.268 

50 

100 

0.237 

0.248 

50 

100 

0.232 

0.245 

100 

0.272 

solvent  for  the  electrolyte. 
N/2  KC1  N/4  KC1  * N/4  KC1* 


c 

V 

c 

V 

c 

ir 

0 

0.022 

0 

0.  051 

0 

0.047 

1 

0.024 

2 

0.055 

1 

0.051 

2 

0.028 

4 

0.059 

5 

0.  059 

5 

0.029 

9 

0.067 

10 

0.057 

10 

0.035 

15 

0.  075 

15 

0.076 

15 

0.041 

20 

0.080 

21 

0.082 

21 

0.  043 

25 

0.085 

26 

0.098 

27 

0.049 

50 

0.106 

50 

0.108 

50 

0.  067 

100 

0.127 

100 

0.129 

N/l 

.8  KC1 

N/32  KC1 

N/32  KC1 

c 

V 

c 

V 

c 

V 

0 

0.120 

0 

0.140 

0 

0.151 

1 

0.121 

2 

0.144 

1 

0.153 

4 

0.124 

5 

0.148 

5 

0.156 

8 

0.128 

8 

0.153 

8 

0.159 

13 

0.132 

14 

0.159 

12 

0.153 

20 

0.136 

20 

0.165 

19 

0.138 

24 

0.139 

24 

0.169 

25 

0.173 

50 

0.161 

50 

0.193 

50 

0.193 

100 

0.176 

100 

0.2  39 

100 

0.208 

N/l28  KC1 

n/255  KC1 

N/2 56  KC1 

c 

V 

c 

V 

c 

V 

0 

0.133 

0 

0.191 

0 

0.193 

1 

0.165 

1 

0.192 

1 

0.194 

4 

0. 169 

4 

0.196 

3 

0.195 

9 

0.177 

9 

0.2  02 

8 

0.2  00 

13 

0.185 

14 

0.207 

14 

0.205 

19 

0.193 

19 

0.212 

18 

0.209 

25 

0.201 

24 

0.214 

50 

0.229 

50 

0.219 

50 

0.230 

100 

0.241 

100 

0.234 

100 

0.241 

N/1024  KC1 
c v 
0 0.249 
$ 0.252 
4 0.254 
10  0.255 
15  0.258 
19  0.262 
50  0.266 
100  0.273 


Typical  curves  from  the  above  data  are  given  in  Plate  N(j»  3. 


160 

* 

VO 

£ 


* 

Ffi- 

<*> 


o 

N 

O 


so 


Zl5 

4 B4+ 

JB 
2 feff 

i BE 

-/oo 


^ o 


«o 


* * s:  * 


Plate  No  3 
Copper  f\nocle 
*KCJ  in  Water 

KCi  in  ¥ /VH*fh/03. 


fJOO 


*5.00 


Po  Tent/  a Is  — > 
$00  .900  ,6  co 


,600 


10 


Table  4.  Copper  Anode  and  Potassium  Iodide  Dissolved  in  N/l 

NII4NO3  Solution. 

N/l  KI  N/2  KI  N/4  ki  N/4  KI  N/«  KI  n/8  KI 


c f 

c 

V 

c 

V 

0 -0.199 

0 

-0.165 

0 

-0.111 

2 -0.198 

2 

-0,163 

2 

-0.110 

5 -0.196 

5 

-0.160 

4 

-0.109 

9 -0.195 

11 

-0.155 

10 

-0.108 

17  -0.192 

14 

-0.153 

14 

-0.108 

21  -0.191 

18 

-0.151 

19 

-0.107 

25  -0.189 

24 

-0.148 

23 

-0.106 

50  -0.  183 

50 

-0.139 

50 

-0.103 

100  -0.172 

100 

-0.123 

100 

-0.100 

N/l6  KI 

N/16  KI 

N/ 32  KI 

c V 

c 

V 

c 

V 

0 -0.076 

0 

-0,075 

0 

-0.063 

2 -0.073 

1 

-0.  073 

1 

-0.052 

5 -0.  072 

4 

-0.  072 

3 

-0.  080 

10  -0.070 

11 

-0. 039 

11 

-0.058 

16  -0.067 

15 

-0.  068 

15 

-0.056 

21  -0.066 

20 

-0.066 

20 

-0.  055 

26  -0.065 

24 

-0.055 

25 

-0.  054 

50  -0.058 

50 

-0.058 

50 

-0.  048 

100  -0.053 

100 

-0.  053 

100 

-0.043 

N/l28  KI 

N/128  KI 

N/256  KI 

C v 

c 

V 

c 

V 

0 -0.015 

0 

-0.019 

0 

-0.001 

2 -0.014 

1 

-0.018 

1 

0.002 

6 -0.012 

r 

-0.  014 

5 

0.  002 

10  -0.011 

10 

-0. Oil 

11 

0.  007 

16  -0.009 

17 

-0.  008 

16 

0.  012 

21  -0.008 

20 

-0.  007 

20 

0.  015 

26  -0.006 

26 

-0. 005 

26 

0.  018 

50  0.002 

50 

0.  0G4 

50 

0.021 

100  0.008 

100 

0.  Oil 

100 

0.  033 

c 

V 

c 

V 

c 

V 

0 0 

-0.112 

0 

-0.098 

0 

-0.  097 

1 

-0,112 

1 

-0,  09 S 

1 

-0.  097 

6 

-0.111 

4 

-0.097 

5 

-0.095 

8 

-0.110 

11 

-0.096 

9 

-0.095 

13 

-0.109 

16 

-0.095 

14 

-0.094 

17 

-0.108 

21 

-0.095 

20 

-0. 093 

23 

-0.107 

25 

-0.094 

24 

-0. 902 

50 

-0.103 

50 

-0.  090 

50 

-0.  090 

100 

-0.099 

100 

-0.  086 

100 

-0.085 

2/32  KI 

N/64  KI 

N / 64  KI. 

c 

V 

c 

V 

c 

V 

0 

-0,062 

0 

-0,  045 

0 

-0,044 

1 

-0.060 

2 

-0  . 044 

2 

-0.043 

6 

-0.058 

5 

-0.043 

5 

-0.042 

10 

-0.057 

10 

-0.  042 

10 

-0. 041 

20 

-0. 054 

IS 

-0.  040 

15 

-0.040 

25 

-0.053 

20 

-0.039 

20 

-0.  039 

50 

-0.047 

25 

-0.  036 

26 

-0.03S 

100 

-0.042 

50 

-0.030 

50 

-0.032 

190 

-0.  024 

190 

-0. 027 

N/256  kI 

N/512  til 

N/512  KI 

c 

V 

c 

V 

c 

V 

0 

0.001 

0 

0.  019 

0 

0.020 

1 

0.008 

2 

0.020 

2 

0.  022 

5 

0.  099 

5 

0.022 

5 

0.  024 

11 

0.019 

10 

0.025 

10 

0.028 

16 

0.021 

15 

0.028 

16 

0. 030 

21 

0.022 

19 

0.090 

20 

9.  032 

26 

0.023 

26 

0.033 

25 

0.034 

50 

0.031 

50 

0.  043 

50 

0.  047 

100 

02037 

100 

0.  059 

100 

O.0S2 

N/1024  KI 


c 

V 

c 

V 

0 

0*  042 

0 

0%  043 

2 

044 

3 

0.044 

4 

0.046 

5 

0.045 

10 

0.  050 

9 

0.047 

15 

0.  054 

15 

0.050 

20 

0.057 

19 

0.052 

25 

0.059 

25 

0.055 

50 

0.  070 

50 

0.067 

100 

0.  093 

100 

0.  089 

Curves  typical  of  the  above  data  are  given  on  Plate  N<j».  4. 


* 


# r 


% • 


* 


11. 

T able  5 

. Copper  Anode  in  an 

Electrolyte  of  Potassium  Chloride 

Dissolved  in  N/l  N84NGP3 

c = current  in 

galvanometer  scale  divisions. 

v = 

electrode 

potentials 

in  volts. 

Note 

: This  Table  differ  from  Table 

No  3 in  that  a different 

series  of  dilutions  are  used. 

/ 

K/4 

KC1 

N/l  KC1 

1/ 10  KC1 

N/10  KC1  N/lOO  KC1 

N/lOO  KC1. 

c 

V 

c V 

c V 

c V 

c V 

c V 

0 

-0.  035 

0 -0.041 

0 0.063 

0 0.068 

0 0.116 

0 0.125 

1 

-9.  032 

1 -0.040 

4 0.073 

3 0.076 

1 0.124 

1 0.129 

8 

-0.024 

9 -0.030 

10  0.083 

9 0.086 

5 0.141 

5 0.148 

13 

-0.020 

14  -0.023 

14  0.091 

15  0.098 

10  0.162 

10  0.164 

20 

-0. 015 

20  -0.018 

19  0.098 

19  0.100 

IQ  0.176 

16  0.178 

24 

-0.010 

25  -0.013 

24  0. 1)04 

24  0.107 

20  0.183 

20  0.184 

50 

-0.010 

50  0.005 

50  0.126 

50  0.133 

25  0.191 

25  0.193 

100 

0.  020 

100  0.021 

100  0.148  100  0.150 

50  0.215 

50  0.218 

100  0.230 

100  0.233 

n/iooo  kcl  u/ioqo 

N/10j000  n/io, 000  n/ioo, 000  n/iog, 000 

e 

V 

c V 

c V 

c V 

c V 

c V 

0 

0.147 

0 0.139 

0 0.160 

0 0.158 

0 0.171 

0 0.171 

1 

0.154 

2 0.153 

2 0.175 

5 0.177 

1 0.170 

2 0.175 

3 

0.105 

4 0.165 

5 0.185 

10  0.202 

3 0.182 

5 0.198 

9 

0.188 

9 0.185 

10  0.200 

14  0.212 

8 0.195 

9 0.203 

15 

0.199 

14  0.199 

15  0.211 

25  0.226 

13  0.208 

15  0.215 

20 

0.207 

19  0.2  06 

19  0.217 

50  0.243 

20  0.217 

20  0.222 

26 

0.212 

25  0.212 

25  0.224 

100  0.250 

24  0.221 

25  0.227 

50 

0.232 

50  0.233 

50  0.241 

50  0.223 

50  0.245 

100 

0.243 

100  0.243 

100  0.250 

100  0.249 

100  0.252 

N/l,000, 000 

e 

V 

c V 

1 

0 

0.152 

0 0.150 

2 

0.161 

2 0.158 

k 

u 

0.181 

5 0.176 

10 

0.102 

10  0.196 

15 

0.212 

15  0.2  09 

20 

0.221 

20  0.217 

24 

0.223 

50  0.241 

50 

0.-242 

100  0.250 

100 

0.251 

f - 

Curves 

typical  of  the  above 

data  are 

given  on 

Plate  No  5. 

I 


10  0 


50 


vo 

* 

N 

V) 

' "x 


Aj 


S 

5 

5 

\ 

>s 

* 

\. 

\ 

V 

;> 


US 

20 

tf 

to 


t 


Aj 

V- 

*i' 


V) 


Pot?  nl7'a/$-> 

-2,00  -700 


+ 

1 

o 

o 

A->  vj 

f) 

V 

‘-I 

/ 

'x. 

_ / 

< 

>JO  / 

l 

J 

/ 

1 

/ 

I 1 "V 

Poten 

AJ 

V 


Plate  No  5. 

Copper  A/iod& 

KCl  m f-  kl<.lf03 


+JOO  9 -i-JZOO  ll  1 l$0O 


12 


Table  6.  Copper  Anode  in  an  Electrolyte  of  Potassium  Bromide 

Dissolved  in  N/l  NH4N03. 


c = current  in  galvanometer  scale  divisions, 
v = electrode  potenrials  in  volts. 


N/l 

N/l 

n/io 

N/lO 

n/ioq 

N/l  00 

c 

V 

c V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

-0.071 

0 -0.070 

0 

0.047 

0 

0.044 

0 

0.101 

0 

0.096 

1 

-0,069 

1 -0,039 

3 

0.  954 

1 

0.  051 

1 

0.109 

2 

0.103 

5 

-0.066 

S -0.063 

9 

0.062 

4 

0.  055 

5 

0.118 

5 

0.109 

10 

-0.063 

10  -0.061 

15 

0.07  0 

9 

0.065 

10 

0.139 

9 

0.139 

15 

-0.061 

15  -0.058 

19 

0.  075 

15 

0.074 

15 

0.152 

15 

0.152 

19 

-0.057 

2 0 -0.056 

25 

0.082 

20 

0.078 

20 

0.131 

20 

0.164 

24 

-0.055 

25  -0.052 

50 

0.105 

25 

0.  084 

25 

0.169 

25 

0.174 

50 

-0.038 

50  -0.041 

100 

0.127 

50 

0.106 

50 

0.199 

50 

0.2  03 

100 

-0.024 

100  -0.028 

100 

0.129 

100 

0.207 

100 

0.210 

n/iooo 

n/iooo 

N/lO 

, 000 

N /lOC 

v* 

c 

c 

o 

c 

V 

c V 

c 

V 

c 

V 

c 

V 

c 

V 

D 

0.159 

0 0.142 

0 

0.155 

0 

0.148 

0 

0.168 

0 

0.149 

4 

0.165 

1 0.148 

1 

0.137 

2 

0.160 

5 

0.173 

5 

0.179 

3 

0.177 

3 0.165 

n 

O 

0.175 

5 

0.175 

10 

0.190 

9 

0.197 

6 

0.182 

5 0.168 

n 

XJ> 

0.181 

10 

0.192 

14 

0.200 

15 

0.213 

9 

0.191 

10  0.183 

10 

0.195 

15 

0.2  03 

19 

0.211 

20 

0.219 

16 

0.203 

15  0.196 

15 

0.2  04 

19 

0.212 

25 

0.224 

25 

0.225 

20 

0.2  09 

20  0.208 

20 

0.212 

25 

0.219 

50 

0.241 

50 

0.243 

25 

0.212 

25  0.213 

25 

0.218 

50 

0.237 

100 

0.252 

100 

0.254 

50 

0.233 

50  0.238 

50 

0.233 

100 

0.251 

100 

0.244 

100  0.246 

100 

0.248 

N/l, 000, 000 

e 

V 

c V 

0 

0.171 

0 0.173 

i. 

0.180 

1 0.1S0 

4 

0.189 

4 0.190 

8 

0.201 

8 0.199 

14 

0.211 

14  0.210 

20 

0.219 

19  0.217 

25 

0.223 

24  0.222 

50 

0.241 

50  0.239 

100 

0.253 

100  0.251 

Curves  typical  of  the  above  data  are  given  on  Plate  No. 5 


13. 

Table  7.  Copper  Anode  in  an  Electrolyte  Potassium  Iodide 

1)  issolved  in  N/l  NH4NO3. 

c = current  in  galvanometer  scale  divisions, 
v = electrode  potentials  in  volts. 

Note:  This  Table  differs  from  Table  No .4  in  that  a different 
series  of  dilutions  are  used. 


N/l  , 

N/l 

n/io 

n/io 

N/lOO 

N/lOO. 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

-0.214 

0 

-0.212 

0 

-0.  093 

0 

-0.095 

0 

-0.025 

0 

-0.025 

2 

-0.213 

1 

-0.210 

1 

-0.092 

1 

-0.  094 

1 

-0.023 

1 

-0.024 

7 

-0.212 

7 

-0.209 

6 

-0.  091 

3 

-0.091 

3 

-0.  019 

4 

-0.021 

10 

-0.211 

10 

-0.207 

9 

-0.  088 

9 

-0.  089 

11 

-0.016 

11 

-0.  018 

19 

-0.209 

18 

-0.2  05 

15 

-0.  088 

15 

-0.  087 

15 

-0.013 

15 

-0.03  7 

24 

-0.207 

24 

-0.203 

19 

-0.  085 

19 

-0.  085 

21 

-0.012 

20 

-0.  014 

50 

-0.2  02 

50 

-0.198 

24 

-0.  083 

24 

-0.083 

26 

-0.007 

25 

-0.  012 

100 

-0.192 

100 

-0.187 

50 

-0.  073 

50 

-0.  077 

50 

-0. 001 

50 

-0.  004 

100 

-0.  072 

100 

-0.  069 

100 

-0.008 

100 

-0.  002 

N/ 

1000 

N/l 000 

N/l 

0 

0 

0 

0 

N/l 

.0, 000 

N/lOO 

,000 

• 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V V 

c 

V 

0 

0.057 

0 

0.  056 

0 

0.108 

0 

0.108 

0 

0.128 

0 

0.133 

1 

0.06  0 

1 

0.  057 

1 

0.111 

1 

0. 117 

1 

0.131 

1 

0.147 

5 

0.035 

6 

0.032 

5 

0.117 

4 

0.125 

4 

0.145 

4 

0.161 

10 

0.  067 

11 

0.  036 

10 

0.136 

9 

0.139 

10 

0.170 

10 

0.184 

15 

0.073 

16 

0.  067 

15 

0.147 

15 

0.150 

15 

0.189 

15 

0.197 

20 

0.075 

21 

0.072 

21 

0.158 

21 

0.162 

20 

0.198 

20 

0.205 

23 

0.078 

25 

0.  074 

25 

0.139 

25 

0.172 

50 

0.213 

25 

0.211 

50 

0.090 

50 

0.  087 

50 

0.223 

50 

0.225 

100 

0.243 

50 

0.234 

100 

0.102 

100 

0.  097 

100 

0.243 

100 

0.238 

100 

0.245 

N/l, 000, 000, 


e 

V 

c 

V 

0 

0.179 

0 

0.173 

1 

0.181 

1 

0.177 

4 

0.191 

4 

0.188 

10 

0.2  01 

9 

0.199 

15 

0.211 

15 

0.212 

21 

0.216 

20 

0.216 

25 

0.220 

25 

0.222 

50 

0.238 

50 

0.245 

100 

0.252 

100 

0.255 

Curves  typical  of  the  above  data  are  given  on  i-\Late  N<p.  7. 


* 


-2.00  3 -J00  o -fJOO  -tjLOO  +200 


14. 

Table  8.  Mercury  Anode  in  an  Electrolyte  of  Potassium  Chloride 
Dissolved  in  N/l  NH4NOs. 

c = current  in  galvanometer  scale  divisions. 


1 

v = electrode  potentials 

in  volts. 

N/l 

N/l 

N/10 

N/10 

n/ioo 

N/l 00. 

c 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

0.244 

0 

0.240 

0. 

0.316 

0 

0.318 

0 

0.346 

0 

0.345 

1 

0.248 

1 

0.245 

1. 

0.341 

1 

0.338 

1 

0.384 

1 

0.386 

4 

0.257 

5 

0.258 

4 

0.356 

4 

0.357 

7 

0.412 

6 

0.409 

9 

0.265 

9 

0.2G5 

13 

0.370 

11 

0.368 

10 

0.416 

10 

0.416 

14 

0.270 

14 

0.270 

21 

0.371 

10 

0.373 

15 

0.424 

16 

0.424 

26 

0.278 

50 

0.288 

50 

0.371 

20 

0.377 

20 

0.430 

21 

0.428 

60 

0.289 

100 

0.296 

100 

0.377 

26 

0.378 

25 

0.432 

27 

0.433 

100 

0.296 

50 

0.378 

50 

0.432 

50 

0.438 

100 

0.380 

100 

0.435 

100 

0.435 

N/l 000 

n/iqoo 

n/10,  000 

n/io, 000 

N/l 00, 000 

c 

v 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

0.390 

0 

0.388 

0 

0.386 

0 

0.384 

0 

0.392 

0 

0.391 

1 

0.405 

1 

0.405 

2 

0.404 

2 

0.410 

1 

0.412 

1 

0.411 

7 

0.40  0 

7 

0.430 

6 

0.427 

8 

0.432 

4 

0.430 

3 

0.427 

1C 

0.437 

10 

0.437 

10 

0.437 

11 

0.439 

10 

0.449 

10 

0.448 

15 

0.445 

15 

0.446 

16 

0.447 

15 

0.447 

15 

0.458 

15 

0.461 

20 

0.452 

21 

0.455 

20 

0.454 

20 

0.455 

20 

0.469 

20 

0.47  0 

25 

0.459 

25 

0 . 46  0 

25 

0.462 

25 

0.463 

25 

G#477 

25 

0.480 

50 

0.490 

50 

0.490 

50 

0.512 

50 

0.509 

50 

0.515 

50 

0.519 

100 

0.500 

100 

0.503 

100 

0.538 

100 

0.542 

100 

0.541 

100 

0.545 

N/l, 

000, 000. 

c 

V 

c 

V 

0 

0.395 

0 

0.399 

1 

0.420 

1 

0.420 

7 

0.445 

4 

0.436 

10 

0.454 

10 

0.454 

15 

0.465 

15 

0.465 

20 

0.475 

20 

0.475 

25 

0.481 

25 

0.483 

50 

0.523 

50 

0.521 

100 

0.547 

100 

0.557 

Curves  typical  of  the  above  data  are  given  on  Plate  No. 8 


* 


♦ +- 


♦ 


10  o 


\n 

O 

vj 


CQ 


<5 

V 


CO 


^ *i: 


*) 

f 

% 

o 

t: 

■s 

50^ 

s 

■s 

$ 

* 

< 

e 


t 


is 

Z6 

PS 

/o 

$ 


-t/ec 


i,Zoo 


G 

C 

( 

I 

1 

+.3oo 


-tyoo 


FbT?rtT/'a/s 

*5oo 


-> 


+.4,00 


P/ate  No  9. 

Mercury  Anode 

K8r  ,n  MH+N03 


16 


Table  10.  Mercury  Anode  in  an  electrolyte  of  Potassium  Iodide 

Dissolve  in  N/l  NH4NCP3. 

c = current,  in  galvanometer  scale  divisions. 


v = electrode  potentials  in  volts 

1 • 

N/l 

N/l 

N/2 

N/2 

N/4 

N/4 

c i 

c V 

c 

V 

c 

V 

c 

V V 

c 

V 

0 -0.142 

0 -C. 143 

0 

-0.107 

0 

-0.108 

0 

-0.069 

0 

-G.  069 

4 -0.141 

5 -0.142 

6 

-0.106 

4 

-0.10$ 

6 

-0.067 

5 

-0.068 

10  -0.141 

10  -0.141 

10 

-0.105 

9 

-0.106 

8 

-0.  067 

8 ' 

-0.067 

15  -0.140 

15  -0.140 

14 

-0.104 

13 

-0.105 

12 

-0.066 

16 

-0.  065 

20  -0.139 

2 0 -0.139 

19 

-0.104 

21 

-0.103 

20 

-0.  064 

20 

-0.  004 

24  -0.138 

25  -0.138 

26 

-0.102 

26 

-0.102 

24 

-0.063 

0 n 

-0.  063 

50  -0.135 

50  -0.135 

50 

-0.  099 

50 

-0.  098 

50 

-0.058 

50 

-0.058 

100  -0.130 

100  -0.130 

100 

-0.093 

100 

-0.095 

100 

*0.054 

100 

-0.056 

N/8 

Iff/8 

N/l6 

N/16 

N/32 

N/32 

c v 

c V 

c 

V 

c 

V 

c 

V 

c 

V 

p -0.040 

0 -0.040 

0 

-0.  009 

0 

-0.011 

0 

0.021 

0 

G.  022 

1 -0.039 

1 -0.040 

1 

-0. 009 

1 

-0.011 

1 

C.021 

1 

0.  022 

4 -0.039 

4 -0.039 

3 

-0.008 

4 

-0.010 

4 

0.  023 

4 

0.023 

9 -0.037 

10  -0.038 

9 

-0.  006 

10 

-0.008 

10 

G.  025 

10 

0.  0^5 

15  -0.036 

15  -0.036 

14 

-0. 004 

14 

-0.  006 

15 

0.028 

16 

0.  028 

2 0 -0.034 

19  -0.085 

19 

-0. 002 

19 

-0. 

19 

0.  029 

2 0 

0.030 

25  -0.033 

25  -0.034 

26 

-0. 000 

25 

-0.  003 

25 

0.  032 

24 

0.031 

50  -0.026 

50  -0.028 

50 

0.  007 

50 

. 

50 

0.041 

50 

0.040 

100  -0.019 

100  -0.C21 

100 

0.018 

100 

0.  012 

100 

0.049 

100 

0.  048 

N/64 

N/64 

N/128 

N/128 

N/2  56 

N/2  56 

c V 

c V 

c 

V 

c 

V 

c 

V 

c 

V 

0 0.045 

0 0.046 

0 

0.  075 

0 

0.  073 

0 

0.093 

0 

Os  094 

1 0.048 

1 0.046 

1 

0.077 

1 

0.  078 

1 

0.097 

1 

0.098 

4 0.048 

5 0.049 

4 

0.  08  0 

4 

0.  081 

5 

0.105 

5 

0.107 

10  0.051 

10  0.051 

9 

0.  086 

10 

0.  086 

11 

0.113 

10 

0.113 

14  0.052 

15  0.054 

14 

0.  089 

15 

0.089 

16 

0.119 

15 

0.118 

18  0.054 

19  0.056 

19 

0.  093 

19 

0.093 

19 

0.121 

19 

0.122 

26  0.057 

24  0.057 

25 

0.097 

24 

0.  095 

50 

0.140 

50 

0.143 

50  0.066 

50  0.067 

50 

0.110 

50 

0.109 

100 

0.151 

100 

0.153 

100  0.076 

10  0 0.077 

100 

0.123 

100 

0.181 

N/l  .024 

N/l 024 

N/l  0,-000 

N/l 0,000 

N/lOO, 000. 

c V 

c V 

c 

V 

c 

V 

c 

V 

c 

V 

0 0.140 

0 0.140 

0 

0.2  00 

0 

0.202 

0 

0.26  0 

0 

0.262 

1 0.144 

1 0.144 

1 

0.214 

1 

0.209 

1 

0.305 

1 

0.304 

5 0.158 

5 0.158 

6 

0.238 

5 

0.232 

5 

0.419 

4 

0.415 

10  0.166 

10" 0.167 

10 

0.260 

10 

0.252 

11 

0.430 

11 

0.438 

14  0.174 

15  0.174 

19 

0.314 

20 

0.296 

15 

0.448 

16 

0.443 

20  0.179 

2 0 0.177 

24 

0.426 

24 

0.417 

20 

0.4-57 

20 

0.453 

50  0.198 

50  0.194 

50 

0.494 

50 

0.482 

27 

0.467 

28 

0.463 

100  0.205 

100  0.206 

100 

0.531 

100 

0.523 

50 

0.514 

50 

0.504 

100 

0.547 

100 

0.538 

Continued 

on  Page  17 . 

too 

t 

*-> 

o 

L ^ 
«0 


"3 

*0 

f$ 

% 

C' 

<a 

* 

N> 

I 

V 

v 


f 


2$ 

26 

*6 

/6 

s 

-ZQO 


Plate  No  iO. 
Mercury  Anode 
f<I  jn  fWm/Os 


+JOO 


t.doo 


/^o/&/7t7ajm  r!  H jz 
fj-oo  +.5oc>  15  fl^oo 


17 


Table  10.  continued 


N/l, 

000, 

000. 

N/n 

-I  o 

> JL/'v 

N/512 

c 

V 

c 

V 

e 

V 

c 

V 

0 

0.382 

0 

0.384 

0 0. 

0.120 

0 

0.116 

3 

0.4-25 

1 

0.404 

i 

0.124 

1 

0.121 

S 

0.433 

6 

0.428 

6 

0.137 

6 

0.133 

11 

0.444 

10 

0.439 

10 

0.142 

10 

0.140 

14 

0.453 

16 

0.449 

15 

0.148 

15 

0.146 

20 

0.462 

21 

0.457 

20 

0.152 

19 

0.150 

25 

0.471 

26 

0 . 466 

50 

0.166 

50 

0.165 

50 

100 

0.518 

0.561 

50 

100 

0.506 

0.538 

100 

0.178 

100 

0.173 

Curves  typical  of  the  above  data  are  given  on  Plate  No. 10. 

» , 

Table  11-  Mercury  Anode  in  an  Electrolyte  of  Suphuric  Acid 

in  Water. 


c = current,  in  galvanometer  scale  divisions* 
v = electrode  potentials  in  volts. 


N/2 

N/2 

N/4 

N/4 

N/8 

N/8 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

c 

V 

0 

0.522 

0 

0.525 

0 

0.552 

0 

0.548 

0 

0.563 

0 

0.561 

1 

0.550 

1 

0.  r28 

1 

0.567 

1 

0.570 

1. 

0.592 

1 

0.583 

4 

0.563 

2 

0.542 

4 

0.596 

5 

0.601 

3 

0.617 

3 

0.608 

9 

0.594 

4 

0.552 

8 

0.624 

16 

0.637 

14 

0.644 

12 

0.642 

14 

0.621 

10 

0.589 

14 

0.638 

20 

0.641 

IS 

0.649 

19 

0.651 

18 

0.630 

15 

0.622 

20 

0.645 

25 

0.650 

24 

0.655 

24 

0.656 

24 

0.637 

24 

0.638 

25 

0.651 

50 

G.  659 

50 

0.669 

50 

0.659 

50 

0.654 

50 

0.657 

so 

0.659 

100 

0.675 

100 

0.685 

100 

0.686 

100 

0.664 

100 

0.667 

100 

0.674 

N/l6 

N/16 

N/32 

N/32 

e 

V 

c 

V 

c 

V 

c 

V 

o 

2.558 

0. 

0.567 

0. 

0.555 

0 

0.551 

l 

. 0.589 

1 

0.585 

1 

0.557 

1 

0.572 

5 

0.621 

3 

0.618 

7 

0.633 

6 

0.633 

8 

0.639 

9 

0.638 

1® 

0.643 

10 

0.650 

11 

0. 646 

15 

0.650 

15 

0.652 

14 

0.656 

15 

0.651 

20 

0.657 

20 

0.658 

19 

0.665 

18 

0.655 

24 

0.661 

25 

0.664 

25 

0.671 

26 

0.660 

50 

0.680 

50 

0.691 

50 

0 • 696 

50 

0.671 

100 

0.707 

100 

0.715 

1 00 

0.720 

Curves  typical  of  the  above  data  are  given  on  Plate  No. 11. 


f.ioo  +.30°  +4-00  -fSoo  -f  loo  fjoo  t.goo 


P/ate  No  tl . 
/Mercury  Anode 
Ho.  50^  in  Water 


18 


4 

Table  12  Electrode  Potentials  at  Zero  Current. 


Anode 

Copper . 

Mercury 

Electrolyte 

KC1  • 

KBr . KI . 

KC1. 

KBr. 

KI. 

Dilutions 

N/l 

-0.038 

-0.070  - 0.213 

0.242 

0.096 

-0.142 

N/2 

-0.108 

N/4 

-0.069 

n/s 

-0.040 

n/io 

0.  065 

0.045  -0.094 

0.317 

0.198 

N/l6 

-0.010 

N/32 

0.021 

N/64 

0.  045 

N/l  00 

C.  120 

0.098  -0.025 

0.346 

0.269 

f't.  r- 

* i 

N/128 

C.  075 

N/256 

0.094 

N/512 

0.118 

N/l 000 

0.143 

0.15C  0.056 

0.389 

0.324 

N/l 024 

0.140 

N/10, 000 

0.159 

0.151  0.108 

0.385 

0.370 

0.201 

N/lOO, 000 

0.171 

0.159  0.130 

0.391 

0.260 

N/l, 000, 000 

0.151 

0.172  0.151 

0.397 

0.374 

Curves  on 

Plate  No 

.12  show  the  relation 

between 

f 

the  electrode 

potentials  of  Copper  at  zer<p  current  and  the  logarithms  of  the 
dilutions 

Curves  on  Plate  No. 13  show  the  relation  between  the  electrode 
potentials  of  Mercury  at  zero  current  and  the  logarithms  of  the 
dilutions . 


Plate  No  12. 

Copper  Anode 
~Lei'0  dvr  rent  Pofonttcih 

and 

Di  fvTio  n . 


t 

I 


I 

/£> 


\ 

/OP 


I 

/ OOP 


l 

/oooo 


/ooooo 


I,  0OO/OOO  Oil  Upon  in  liters 


J. 


4~  ^ S 


6 Pocjari  fhm  of  Dilution 


. 


■ 


PJa/te  No  /3. 
Mercorxj  Anode 

Zero  Current  PotenTia./s 

an 
Dtlv'i 


and 
'77 on . 


-X- 

-tr 


to 


/oo  1600  JOOOO  /OQ  Ooo  /oooooo  Dilutions  :n Lifer* 
3 V $ * Logarithm  o of Dt/ufion^ 


19 


DISCUSSION. 

(l)  Reaction  Potentials  for  Zero  Current.  The  electrode  potent- 
ial measured  for  zero  current  is, to  be  sure,  nothing  more  than  the 
potential  for  that  electrode,  as  usually  measured  under  static  con- 
ditions. The  very  first  reading  is  never  very  definite;  only  after 
a certain  minimal  current  has  passed  can  it  be  said  to  assume  a def- 
inite value.  The  potential  values  for  the  passage  of  a given  current 
seem  quite  definite,  a fact  fully  substantiated  by  duplicate  determ- 
inations. Of  course,  if  an  appreciable  amount  of  current  is  allowed 
to  traverse  the  cell,  thereby  increasing  the  metalic  ion  concentra- 
tion of  the  electrolyte,  the  potential  will  be  displaced  to  the 
right  in  a corresponding  degree- 

That  the  potential  for  zero  current  should  be  somewhat  uncer- 
tain is  to  be  expected.  It  will  be  seen  from  the  Nernst  formula  for 
potential,  E = RT/nF  times  log  P/p  , that  E can  have  a definite 
value  only  when  p is  definite.  With  the  passage  of  a minute  current 
the  cation  concentration,  at  least  in  the  neighborhood  of  the  elect- 
rode, takes  a positive  value, so  that  the  upper  portion  of  the  curve 
may  be  projected  downward  giving  a zero  value  that  is  easily  repro- 
ducible 

The  following  figures  show  the  comparison  of  reaction  poten- 

, 

tials  with  the  ordinary  electrode  potentials  for  solutions  saturated 
with  the  reaction  products.  For  copper  electrode  in  0.05N  KCl,the 
reaction  potential  is  D.B85  volts  and  the  electrode  potential  is 
0.214  volts,  for  0.5N  KBr  the  reaction  potential  is  0.G55  volts 
and  the  electrode  potential  is  0.132  volts.  For  a mercury  electrode 
in  N KC1  the  reaction  potential  is  0.240  volts  and  the  electrode 


. 


■ 


, 


20. 

potential  is  0.283,  for  0.1N  KC1  the  reaction  potential  is  0.312 
and  the  electrode  potential  is  0.334  volts,  for  0.1N  j^Kr  the  react- 
ion potential  is  0.198  while  the  electrode  potential  is. 201  volts. 

/ 5 /<?S s 

In  every  case  the  reaction  potential ^ than  that  of  the  corresponding 
electrode  potential  with  a solution  saturated  with  the  copper  or 
mercury  salt  formed.  The  less  soluble  the  salt  (e.g.  Cuofrp  ,Hgr>Br2 ) 
the  less  the  difference. 

(9)  Products  of  the  Anode  Reaction.  The  reaction  potentials, 
as  above  stated,  are  somewhat  below  the  electrode  potentials  meas- 
ured against  a solution  saturated  with  the  reaction  product.  It  has 
been  assumed  that  the  reaction  products  are  always  salts  of  the  low- 
er valence  of  - he  electrode  metal;  that  is  cuprous  and  mercurous 
compounds.  This  assumption  is  amply  justified  by  the  fact  that  the 
electrode  potential  for  the  corresponding  cupric  and  mercuric  salts 
are  far  above  the  electrode  potentials  just  mentioned.  Furthermore, 
electromotive  force  measurements  show  that  more  work  is  necessary 
for  the  formation  of  the  ions  of  the  higher  valence.  Hence  it  is 
concluded  that  copper  and  mercury  dissolve  with  the  formation  of 
cuprous  and  mercurous  salts  as  the  primary  products. 

(3)  Form  of  the  Current  Potential  Curves.  Reference  to  Plates 
1 to  11  will  show  two  general  types  of  graphs.  First,  graphs  that 
are  almost  straight  lines  cutting  the  potential  axis  at  angles  very 
nearly  right  angles;  e.g.,  mercury  with  N KC1  (Plate  No.7).  Second, 
graphs  that  show  a more  or  less  marked  flexure, as,  mercury  with 
HgSOj  {Plate  No.ll.).  In  this  latter  case  the  angle  made  with  the 
potential  axis  is  fairly  acute.  In  cases  of  high  dilutions,  the 
curves  of  solutions  containing  the  anion  of  insoluble  salts  also 


. — 

» • . 

. . 


21 


approach  this  second  type.  For  example  see  mercury  in  N/l00,000  KI 
Plate  No. 10.  The  explanation  of  this  second  type  of  curve  is  in  the 
fact  that  the  potential  of  the  electrode  increases  with  the  concen- 
tration of  the  metalic  ion.  For  practically  insoluble  salts  this  lim 
iting  potential  is  reached  ina  very  short  time, so  that  the  potential 
increases  very  slightly  above  the  reaction  potential.  With  more  sol- 
uble salts,  however,  considerable  current  must  pass  before  the  cat- 
ion concentration  reaches  the  maximum, as  indicated  by  the  flexture 
of  the  curve.  The  fact  that  in  high  dilutions  of  insoluble  salts 
like  mercurous  chloride  behave  in  this  way  is  due  to  the  presence 
of  some  ’’inert"  solute  which  has  been  added  in  order  to  maintain  the 
conductivity  of  the  solution.  These  solutes  increase  the  solubility 
of  the  more  insoluble  salt  by  a metathetical  reaction, sometimes 
called  the  "uncommon  ion  effect", for  example  the  reaction, 

Hg2Cl p-f  2NH4NO3  = Ilg^NOoJo  + 2NH4CI « Consequently,  the  concentration 
of  the  cation  in  the  solution  may  be  greatly  increased. 

( / ) The  Relation  between  Reaction  Potential  and  Concentration. 
Plates  No. 12  and  No. 13  shows  the  relation  obtained  between  reaction 
potential  and  concentration.  According  to  Nernst  formula  the  graph 
showing  the  relation  between  the  logarithm  of  the  dilution  and  the 
reaction  potential  should  be  a straight  line.  The  curves  so  obtained 
only  approximate  strait  lines  in  sone  of  their  parts. 

(5)  The  Existance  of  Definite  Ionization  Potentials.  Thermodynac*- 
ic  considerations  lead  to  the  assumption  that  the  direct  ionization 
of  a metal  should  be  independent  of  the  anions  present  am  the  elect- 
rolyte, and  should  depend  only  on  the  nature  of  the  metal  and  its 
electric  charge.  This  would  mean  that, no  matter  what  the  electrolyte 
might  be  or  what  its  concentration  value, all  solutions  of  the  same 


<3 

. 

_ 

. 


. 


■ 


■ 


. 

. 


22. 


metal, and  sufficiently  high  currents,  should,  show  a common  reaction 
potential.  This  is  what  Reedy  found  in  the  case  of  silver;  that  is 
the  current  potential  curves  for  all  solutions  showed  a flexure  at 

about  0.520  volts  (refered  to  N hydrogen  electrode  = 0.0  volts). 

' is  y,  is  the  rote*  tial 

That  is  to  say,  this  is  the  potential  necessary  to  send  silver  ions 

Ag  , into  a solution  against  an  osmotic  pressure  for  silver  ions 
equal  to  zero. 

Thermodynamics,  on  the  other  hand,  teaches  that  the  voltage 
necessary  to  send  an  infinitesimal  amount  of  cations  into  an  elect- 
rolyte containing  none  of  these  ions  is  less  than  zero.  This  follow 
s directly  from  the  usual  method  of  equating  electrical  and  osmotic 
work.  That  is,  E = -RT/nF  times  log^  P/p,  where  P is  the  ionic  sol- 
ution tcntion  and  p is  the  osmotic  pressure  of  the  ions.  Putting  p 
equal  to  zero  then  E must  he  less  than  zero,  meaning  that  no  work 
would  be  required.  This  is  evidently  another  case  where  thermodynam- 
ics gives  us  no  help,  since  is  one  of  false  and  not  actual  equilib- 
rium. It  seems  that  ionization  potential  may  be  analogous  to  kind- 
ling temperature  in  combustion.  The  metal  may  send  ions  into  the 
solution  at  voltages  lower  than  the  critical  ionization  potential, 
but  the  action  is  negligibly  small.  With  increase  in  voltage,  a pot- 
ential is  reached  where  the  current  shows  a very  marked  increment, 
and  a state  of  equilibrium  between  the  metal  and  solution  is  rapid- 
ly approached. 

That  no  such  ionization  potentials  have  been  found  in  this 
work  for  copper  and  mercury  anodes  may  be  due  to  the  fact  that  t 
these  potentials  are  higher  than  any  of  the  potentials  that  may  be 
attained  with  electrolytes  of  ordinary  concentration.  On  the  other 
hand.,  the  claim  of  certain  investigators  that  chemical  activity 


' 


- 

- 


23. 

is  inherent  in  the  anions  alone  has  not  been  definitely  disproved, 
it  is  insisted  that  such  a theory  does  not  seem  particularly  con- 
vincing. 

Summary . 

1.  Reaction  potentials  of  copper  and  metallic  mercury  have  been 
measured  for  a number  of  the  common  anions  for  dilutions  varying 
from  1 to  1,000,000  liters. 

2.  These  potentials  are  somewhat  less  than  the  potential  values 
measured  directly  by  the  usual  static  method,  usuing  solutions  sat- 
utated  with  the  reaction  products. 

3.  These  reaction  potentials  correspond  to  the  formation  of 
ions  of  the  lower  valence,  vig.  Cuprous, Cut*,  and  Mercurous ,IIg|^ . 

4.  The  graphs  obtained  by  plotting  reaction  potentials  against 
dilutions  are  not  straight  lines  as  would  be  expected  from  the 

N er bs t f o rmu 1 a . 

5.  Aside  from  the  flattening  of  the  potential  dilution-dilution 
curves,  there  is  no  evidence  of  definite  ionization  potentials , such 
as  Reedy  found  in  the  case  of  silver. 


